Ultrasensitive time-resolved fluorescence method for α-fetoprotein

Abstract

We have examined the maximum sensitivity of a newly developed and optimized time-resolved fluorescence immunoassay system. The system, originally described elsewhere (Clin Biochem 1988;21:139-50), has undergone significant improvements in sensitivity through improvements of the labeled reagent used. We have chosen an α-fetoprotein (AFP) assay as a model and used monoclonal "capture" antibodies and monoclonal or polyclonal biotinylated antibodies in "sandwich-type" assay configurations. Streptavidin labeled with the europium chelator 4,7-bis(chlorosulfophenyl)-1,10-phenanthroline-2,9-dicarboxylic acid was used for detection. We can measure as few as 3 × 105 molecules of AFP with the optimized system. We have applied this assay to measure AFP in the serum of normal individuals after a 10-fold sample dilution. We conclude that this system is extremely sensitive and can be used in immunoassay or other applications where biotinylated reagents can be applied.